Tuning range adjustment device



Sept. 6, 1938. w. VAN B. ROBERTS 2 W TUNING R ANGE ADJUSTMENT DEVICE Original Filed March 9, 1933 a b 70 NEXT M IT V STAGE FREOUEATY Q/AL 55m A/GS INVENTOR 4 WALTER 144M 5. Ros/5m BY M. 40m

ATTORNEY UNITED STATES GlFFiCE TUNING RANGE ADJUSTMENT DEVICE Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application March 9, 1933, Serial No.

660,124. Divided and this application Februmy 14, 1936, Serial No. 63,825

2 Claims. (Cl; 25040) My present invention relates to tunable radio A switch device is employed for selectively confrequency circuits, and more particularly to tunnecting and disconnecting the fixed condensers able circuits including fixed tuning adjustment K1 and K2. This switching device in. Fig. 1 comreactance elements, and is a division of my appliprises a terminal a connected to one side of the 5 cation serial No. 660,124, filed March 9, 1933 tuning condenser Cs and a second terminal b patented March 24, 1936 as U. S. P. 2,034,773. connected to one side of the fixed condenser K2,

The object of the present invention is to pro and a movable switch arm 2i connected to the vide a tuning means for a resonant radio fregrid of tube 2G. in Fig. 2, the switch arm H is quency circuit which can readily be changed connected to one side of the tuning condenser from a condition which covers a wide range of C6, the terminal a. is connected to the grid of 10 frequencies to a condition which covers only a tube 20, and the terminal 19 is connected to one narrow band of frequencies with the same range side of the fixed condenser K2. of adjustment of the tuning mechanism. In both Figs. 1 and 2, when the switch arm 21 The novel features which I believe to be charis connected to terminal a the tuning condenser acteristic of my invention are set forth in paris directly connected across the inductance coil 15 ticularity in the appended claims, the invention L6, and the shunt condenser K2 is disconnected. itself, however, as to both its organization and Therefore, the range of tuning will be as great method of operation will best be understood by as the ratio of the square root of the maximum reference to the following description taken in and minimum capacities of the variable conconnection with the drawing in which I have indenser together with tube and coil capacities. 20 (heated diagrammatically v a cu ga With the usual type of variable condenser this izations whereby my invention may be carried range of frequencies would be about 3:11. into effect. With the switch arm 2! on terminal I) the In the drawing: maximum capacity across the inductance coil L6 25 Figs. 1 and 2 show alternative embodiments of is reduced by series condenser K1, while the mini- 25 the basic principle of the present invention apmum capacity is increased by the condenser K2. plied to a band spreader device for tunable radio By properly choosing the values of K1 and K2 the frequency circuits and, range of. variation of circuit capacity may be Fig. 3 graphically illustrates the operation of made as small as desired. the arrangement of Figs. 1 and 2. Fig. 3 graphically shows how the frequency of 30 The basic principle of the p es t v tio is the resonant circuits of Figs. 1 and 2 vary with utilized to provide a tuning means W c ca tuning condenser adjustment according as the r y be han d from a ndition Which c v s switch arm 21 is in position a or position b. With a wide range of frequencies to a condition. which the capacities K1 and K2 so chosen as to make the I covers only a narrow band of frequencies with minimum capacity across coil Ls greater in switch 35 the same range of a justment of the tuning position 2) than in a, and the maximum capacity mechanism. across coil Ls less in b than a, it is obvious that In both Figs. 1 and 2, the grounded antenna the curves of Fig. 3 mustcross each other, and circuit A2 is coupled to the input electrodes of this position of the crossing may be chosen at an amplifier u 23 y means o a d o ewill by properly choosing the relative values of 40 q y transformer the Secondary coil Le of K1 and K2. For example, if it is desired in the which is connected between the grid and cathode case of Fig. 1 to have the crossing point occur 0f the amplifier tube. The anode a d Ca hode when the variable capacity has a value Cm, all of the amplifier tube may be coupled to a sucthat is necessary is to make ceeding amplifier stage of any well known type 2 45 of receiver. Such a receiver may be of the tuned radio frequency amplifier type, a superhetero- Kltcm dyne receiver, or even a super-regenerative re- Th arrangements shown in Figs. 1 and 2 are ceiver. The variable tuning condenser Ce is conparticularly adapted to amateur reception. The

nected across the fixed inductance coil Le. Howamateur frequency bands are located in har- 50 ever, a large fixed condenser K1 is connected subm i relation with each other. That is to say, stantially in series with the variable condenser h b d i t approximately twice t i Cs, While a small fixed condenser K2 is arranged ue e of the preceding one. If now a separate for connection substantially in shunt With the coil is provided for each band, the range of variable tuning condenser Ce. tuning available with an ordinary condenser is 5 at least 2:1 and, hence, is such as to make possible reception of all frequencies between the amateur bands, when desired, by setting the switch arm 2| on position a.

However, when receiving messages lying within the amateur bands, the switch is used on position I), the condensers K1 and K2 being chosen to have such values as will cause the frequencies in the amateur band to be spread out over a considerable portion of the dial adjustment and thus greatly facilitate tuning. When plug-in coils are used for the various bands, it is well to choose the inductances so that for each coil the center of the desired band occurs at C=Cm=the same for each coil. This avoids the necessity to readjust K1 or K2 to center the band on the setting Cm.

While I have indicated and described several systems for carrying my invention into efiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. A resonant network comprising a variable condenser and coil that tune over a wide frequency range, which wide range includes a narraw frequency range, the mid-frequency of said narrow range being secured by adjustment of the variable condenser to a capacity Cm, a fixed condenser K1 in series with said first condenser, and a fixed condenser in shunt with said first condenser, means for selectively disconnecting the condenser K2 from across the first condenser and shorting condenser K1, the capacity of condenser K1 being chosen smaller than capacity Cm, and there existing the following relation whereby the resonant frequency is the same for both switch positions, but the range of tuning is very much less with the condensers K1 and K2 in circuit.

2. In combination, an inductance element, a variable condenser having a sufliciently large ratio of maximum capacity to minimum capacity to resonate said inductance over a relatively large frequency range when operatively associated therewith, a fixed condenser of capacity K1 which is smaller than a Value Cm, switching means for connecting said fixed condenser in series relation with said variable condenser, a second fixed condenser of capacity K2, said switching means being adapted to connect the second fixed condenser in shunt relation to the said variable condenser, the capacity of said second fixed condenser being the capacity Cm being the capacity of the variable condenser when adjusted to resonate the said inductance to the mid-frequency of its range 01 adjustment, whereby the said inductance is resonated to the same mid-frequency when the said variable condenser is adjusted to the value Cm regardless whether the aforesaid switching means is set to connect said fixed condensers effectively with said variable condenser or not, but whereby the range of tuning is reduced by switching said fixed condensers into connection with said variable condenser.

WALTER VAN B. ROBERTS. 

